1. Field of the Invention
The present invention relates to a light-emitting device, a vehicle headlamp, and an illumination apparatus, each of which radiates illumination light in a desired projection pattern.
2. Description of the Related Art
In recent years, research on light-emitting devices is becoming active, which light-emitting devices each use, as an excitation light source, a semiconductor light-emitting element such as a light-emitting diode (LED) or a laser diode (LD) and use, as illumination light, fluorescent light that a light-emitting section containing a phosphor generates upon irradiation with excitation light emitted from the excitation light source. Such technology is also applied to an illumination apparatus such as a vehicle headlamp.
For example, as shown in FIG. 15, a vehicle headlamp 100 disclosed in Japanese Unexamined Patent Application Publication No. 2011-181381 (published on Sep. 15, 2011) includes a metal plate 111, a phosphor 112 which is arranged on the surface of the metal plate 111 and emits light on excitation by blue laser light, a laser light source (not shown) which radiates the blue laser light which enters the phosphor 112, and a reflection suppressing member 113 which is arranged so as to cover the surface of the metal plate 111 surrounding the phosphor 112 and suppresses the reflection of the blue laser light entering from the laser light source. Accordingly, the vehicle headlamp 100 is configured so as to prevent (or reduce) color irregularities and luminance irregularities of the emitted light which are caused by the blue laser light radiated from the laser light source being reflected by the surface of the metal plate 111 surrounding the phosphor 112.
Furthermore, for example, as shown in FIG. 16, the vehicle headlamp 200 disclosed in Japanese Unexamined Patent Application Publication No. 2005-150041 (published on Jun. 9, 2005) includes a semiconductor light-emitting element 201 which emits light, a phosphor 202 provided separated from the semiconductor light-emitting element 201, a lens 210 which concentrates the light generated by the semiconductor light-emitting element 201 onto the phosphor 202, and a reflecting mirror 220 which has an optical center in a position at which the phosphor 202 is provided and radiates the outside of the vehicle headlamp 200 with the light generated by the phosphor 202 according to the light concentrated thereon by the lens 210. As shown in FIG. 17A, the reflecting mirror 220 includes an inclined reflective surface 221 and a horizontal reflective surface 222. Accordingly, as shown in FIG. 17B, as the low beam projection pattern which is formed on a virtual vertical screen provided in a position 25 m in front of the vehicle headlamp 200, a projection pattern 230 is formed which includes a horizontal cutoff line 231 for determining the light-dark boundary in a substantially horizontal direction, and an inclined cutoff line 232 for determining the light-dark boundary in a predetermined inclined direction at an angle of approximately 15° in relation to the horizontal direction. The reflecting mirror 220 is a mirror which is referred to as a multifaceted mirror.
In addition, for example, as shown in FIGS. 18A and 18B, the fiber optic illumination apparatus 300 disclosed in Japanese Unexamined Patent Application Publication No. 2009-043668 (published on Feb. 26, 2009) includes a semiconductor laser 310 which emits excitation light 301, a single fiber 320 which acts as a waveguide for the excitation light 301 emitted from the semiconductor laser 310, a phosphor unit 330 which receives the excitation light 301 emitted from the single fiber 320 and emits fluorescent light of a different wavelength from that of the excitation light 301, and a fiber bundle 340 which acts as a waveguide for at least a portion of the fluorescent light emitted from the phosphor unit 330. The fiber optic illumination apparatus 300 further includes a reflector 350 which reflects, of the reflected scattered light generated by the phosphor unit 330 and the fluorescence emitted from the phosphor unit 330, at least a portion of the light which does not directly enter the entrance region of the fiber bundle 340 toward the entrance region of the fiber bundle 340.
However, in the light-emitting device, the vehicle headlamp and the illumination apparatus of the related art, there is a problem in that the projection efficiency decreases due to a loss of illumination light.
Specifically, in the vehicle headlamp 100 disclosed in Japanese Unexamined Patent Application Publication No. 2011-181381, in order to obtain a projection pattern with a clear edge, the surface of the metal plate 111 surrounding the phosphor 112 is covered with the reflection suppressing member 113. As a result, a portion of the blue laser light entering from the laser light source is shielded. Therefore, the projection efficiency decreases due to a loss of illumination light. In addition, stray light caused by scattering on the surface of the metal plate 111 causes the contrast at the edge to deteriorate. Furthermore, according to optical absorption at the metal plate 111, there is a problem in that the temperature of the metal plate 111 increases, thereby influencing the properties of the phosphor 112, such as changes in chromaticity and intensity.
In addition, in the vehicle headlamp 200 disclosed in Japanese Unexamined Patent Application Publication No. 2005-150041, a multifaceted mirror is used for the reflecting mirror 220. As a result, it is difficult to obtain a projection pattern with a clear edge using a multifaceted mirror, and further, a large reflecting mirror 220 is necessary. Furthermore, there is also a problem in that stray light enters unnecessary regions such as vacancies, that is, the efficiency decreases.
Meanwhile, in order to prevent the loss of illumination light, the fiber optic illumination apparatus 300 disclosed in Japanese Unexamined Patent Application Publication No. 2009-043668 includes a reflector 350 in order to cause, of the reflected scattered light generated by the phosphor unit 330 and the fluorescence emitted from the phosphor unit 330, at least a portion of the light which does not directly enter the entrance region of the fiber bundle 340 to enter the entrance region of the fiber bundle 340. However, since the disclosure of the fiber optic illumination apparatus 300 disclosed in Japanese Unexamined Patent Application Publication No. 2009-043668 only relates to application to an endoscope, there is no mention of application to a projection pattern. Accordingly, the disclosure is insufficient for application to a vehicle headlamp.